1. Field of the Invention
The present invention relates to systems for distributed control with hierarchical supervision of the power grid when using a plurality of self-aware distributed power flow controllers.
2. Prior Art
Most power utilities use centralized energy management systems (EMS) and supervisory control and data acquisition (SCADA) systems for control of the power grid systems. These control systems provide communication and control between any of the following at the various geographically-distributed sub-stations and the centrally-located EMS:
remote terminal units;
breakers;
phase-shifting transformers;
analog and digital sensing devices;
FACTS (Flexible AC Transmission Systems and Sub-systems).
One problem of this type of centralized control is the inherent delay to and from the EMS. This delay can easily reach three to five seconds, and may even be as long as a minute under certain cases. This limits the responsiveness of the EMS-based grid control system to disturbances in the system. The recent inclusion of plurality of distributed power generation, such as local solar generators and wind-farms, have increased the need for fast optimization of power transfer and fast response to disturbances on the grid, a basic necessity for smoother operation of the power grid.
A fixed substation-based response and control system 200 has been proposed for Flexible AC Transmission System (FACTS) for improved control of the power grid. Such a system is shown in FIG. 2. This system provides a better response capability to the disturbances and perturbations of the high-voltage Transmission grid 202 using static synchronous series compensator (SSSC) at substations 204. Though these SSSCs are able to provide fast response to disturbances recognized, it being a non-distributed system, with communication link 207 to central utility 206 for control inputs and data analysis. This limits the capability of the system by adding delays for detection of problem, delays in communication, and delays for decision, before action can be initiated. This reduces the capability for the system for really fast proactive and interactive responses to local-level perturbations and oscillations of the grid from distributed generators 203, loads 205 or disturbances on the HV transmission lines 202 suspended on transmission towers 201 due to current in-balances, wind-related voltage perturbations due to rapid energy injections, or wind-turbine controls-related resonances etc.
Of recent, distributed control of power flow over the high-voltage (HV) transmission lines using distributed impedance injection modules, has been proposed and is being implemented. FIG. 1 is an exemplary block diagram 102 of such distributed control modules that are static inductive- or capacitive impedance-injection modules 100, attached directly to the HV transmission line 108 transferring power from generator 104 to distribution point 106. A safer and more reliable way to attach the modules has been shown to be to suspend the distributed static impedance-injection modules from the transmission towers. These self-aware static inductive or capacitive impedance-injection modules are then able to identify and react very fast to the changes in the power line characteristics of the individual HV transmission lines 108 to which these are attached at a local level. These intelligent devices, are capable of injecting inductive or capacitive impedances on to the HV transmission lines 108 and hence provide the capability to have localized control of line current, and therefore establish a level of power-flow control on the HV transmission lines.